The present invention relates to a self-propelled surface milling machine, preferably in the form of an asphalt-milling machine, snow-milling machine or Surface Miner, having a mill roll which is drivable about a rotational axis, and a mill roll drive comprising at least one electrical motor which is accommodated within the mill roll, wherein stator and rotor of the electrical motor are accommodated within a dust and air-tightly sealed motor housing.
Surface milling machines are continually self-propelled working machines which, with the aid of a rotating roll, crush a layer of asphalt or soil or the like by milling and which commonly continuously proceed with the aid of caterpillars to force the roll into the milling goods. In doing this said roll forms the main operational unit requiring high energy and thus is in need of an appropriate drive. In this regard DE 10 2007 007 996 B4 suggests a diesel-electric drive, wherein the milling roll of a Surface Miner is driven by means of an electrical motor provided with energy by a generator. The references WO 03/058031 A1, DE 10 2008 008 260 A1, DE 10 2007 044 090 A1, DE 10 2007 028 812 B4, DE 199 41 800 C2, DE 199 41 799 C2 or DE 20 2007 002 403 U1 disclose further embodiments as well, wherein instead of electromotoric drives hydraulic drives are also utilized in part which are fed with hydraulic power by an hydraulic pump driven by a diesel engine.
From DE 10 2007 007 996 B4 a Surface Miner having an internal electrical motor drive for the mill roll is known. Here two squirrel cage motors each having an associated planetary gear are accommodated within the mill roll body, such that the mill roll drives are safely protected against external influences and damage by e. g. stones. In order to protect both gear and electrical motor against dust, adjacent front sides of the motor-gear-unit which is seated in a tubular frame part are sealed with pot-shaped housing parts which are brought into dust-tight connection with the support frame by a plug washer.
Having such encapsulated electric drives within the mill roll thermal problems will arise because heat generated in the gear and in the motor will not sufficiently be discharged.
Generally electrical motors are cooled by surface cooling or natural draft cooling having forced-air- or self-ventilation. However, these known methods of cooling do not apply to mobile surface milling machines such as Surface Miners, asphalt-milling machines and the like due to reasons of dust incorporation which may be caused by a mill roll operating in or on the soil. Furthermore, the drive, while in use, might also partially submerse into water, so an embodiment wherein the motor is sealed will be preferred. Moreover, depending on the soil at the operational site, heavy formation and resuspension of dust may be caused by strong flow of air that exits the motor, which might not be acceptable in most applications.
It has thus been considered, to provide aspiration of cooling air through a snorkel type of device on a highest point of the machine, as in this location low formation of dust and hence low incorporation of dust into the motor may be achieved. However, the problem of dust formation by the exiting cooling air is still to be solved.
Avoiding dust formation as far as possible can be achieved by a hermetically sealed motor wherein even exiting cooling air will be captured in a conduit and will be fed into an outlet at an elevated location on top of the machinery. Nevertheless a residual amount of dust will remain in the motor since dust formation is substantial with surface milling machines and aspirating power may not be increased arbitrarily.
Operating with a hermetically sealed motor wherein the air is circulated in a closed circuit air system and is cooled by means of a heat exchanger having an air inlet and outlet on top has been taken into account. Herein, however, a problem will arise in that the large amounts of air required for this will require very large conduit cross sections down to the mill-roll drive and backwards which hardly can be accommodated in limited location and accordingly are difficult to protect against mechanical damage.